While we all were irritated to some extent by the massive amounts of caterpillars in 2001 and 2002–stepping on them, having them climb our fences, houses, cars, gates, and everything else around our homes and farms–there is new evidence that the setae (hair-like projections) on the caterpillars can become embedded in the lining of the alimentary tract (GI tract) of animals and cause inflammation, discovered Neil Williams, DVM, PhD, of the University of Kentucky’s Livestock Disease Diagnostic Center.

Williams performed the examinations and histological examinations of the pigs used in an experiment where the animals were fed Eastern tent caterpillars (ETC) in an effort to cause abortions similar to MRLS (mare reproductive loss syndrome) in broodmares. The abortions did occur as a result of feeding ETC to the pregnant pigs, and the pigs were studied at the Diagnostic Center.

“As we examine tissues, we learn to look for ‘unusual’ things,” said Williams. While examining samples from the alimentary tract (which includes the pharynx, esophagus, stomach, small intestine, and colon), Williams noticed multiple small, localized areas of inflammation in some of the pigs. These were not visible with the naked eye, and he noticed them only in some of the pigs. Williams was “blinded” and didn’t know which pigs had been fed caterpillars. So, he noted in which pigs he found the lesions.

He discovered that all five pigs which had been fed caterpillars had these microgranulomas (small, localized areas of inflammation only able to be seen under a microscope), and none of the pigs that had a regular diet free of ETC had the lesions